Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$93.76	6.580%	$99.9294	$99.93	$99.95	$99.90
Purchase #2	$11.75	6.786%	$12.5474	$12.55	$12.55	$12.50
Purchase #3	$18.29	11.602%	$20.412	$20.41	$20.40	$20.40
Purchase #4	$118.88	9.440%	$130.1023	$130.10	$130.10	$130.10
Purchase #5	$133.74	4.583%	$139.8693	$139.87	$139.85	$139.90
Purchase #6	$23.35	10.729%	$25.8552	$25.86	$25.85	$25.90
Purchase #7	$161.96	3.781%	$168.0837	$168.08	$168.10	$168.10
7 purchase totals =	$561.73		$596.7993	$596.80	$596.80	$596.80